Severely obese women (BMI 35 to 40) with type 2 diabetes mellitus have an increased skeletal mass. They also have an increased fat-free mass, presumably including increased skeletal muscle. These women are continually attempting to lose weight in order to improve their diabetes control. Attempts at weight loss have generally been carried out medically in the past, but severely obese women are undergoing bariatric surgery more and more frequently. With weight loss, by whatever means, medical or surgical, fat mass is lost. In addition, there is some evidence that calcium from bone and skeletal muscle mass is also lost. We plan to investigate the loss of bone mineral and skeletal muscle during weight loss in two groups of women with type 2 diabetes, one group losing weight on a hypocaloric diet and another group losing weight with gastric by-pass surgery. The hypotheses to be tested are that, with weight loss: 1) skeletal muscle will be lost in both groups; 2) bone calcium will not be lost if subjects are appropriately supplemented with calcium and vitamin D; 3) biochemical markers of bone turnover will be elevated; 4) gastrointestinal calcium absorption will be impaired in the surgical group; 5) quality of life will improve in proportion to amount of weight loss. We will study pre-menopausal diabetic women with a BMI range of 35 to 40, aged 25 to 45 years. Measures of body composition using Core A&B biochemical markers, and quality of life will be taken at baseline, 6 months, one year, and two years. The two groups will be compared for changes in these parameters and also for improvement in glucose control (HgbA1c), blood pressure, and blood lipids. Core C will be used for data storage, data analysis, and statistical evaluation of results. With the great incidence of weight loss attempts in this country by severely obese diabetic women, and with the increasing bariatric surgery interventions, whether adverse effects on bone and muscle occur is important in estimating the risk-benefit ratio of such attempts. There are no adequate data on bone loss and one on muscle mass in response to gastric by-pass in type 2 diabetic patients, so that the proposal is timely and has public health importance.